The impacts of supplemental L-threonine in laying hen diets were evaluated. Over three experiments, control hens were fed a corn-soybean commercial layer diet containing 0.56% threonine (Thr). Experimental diets containing 0.66, 0.76, 0.86, and 0.96% Thr were fed for experiment 1. Experimental diets containing 0.76, 0.96 and 1.16% Thr were fed for experiment 2. Experiment 1 and 2 hens were 42 weeks of age. In experiment 3, experimental diets containing 0.76 and 0.96% Thr were fed to aged hens (61 weeks at beginning of experiment). Data collection methods were the same for all three experiments. Beginning and ending hen weight, egg production, and feed consumption data were collected. Egg samples were analyzed for egg weight, yolk and albumen yield, protein, and functionality. In experiments 1 and 2, egg production increased with increasing dietary threonine levels up to 0.76% Thr in the diet and subsequently decreased suggesting a production threshold for the amino acid. Shell cracking strength increased with increasing threonine levels in all three experiments. In experiment 3, shell thickness increased with increasing threonine levels. Albumen protein was significantly increased when hens were fed increased levels of dietary threonine. Angel food cake volume was significantly increased in experiments 1 and 3 with increasing dietary threonine, as were other texture profile parameters. Sponge cake volume was significantly increased in experiments 2 and 3 as a result of increased threonine levels. In experiment 3, yolk gel hardness was significantly increased by increasing the level of dietary threonine. These data clearly indicate a potential important impact on egg composition and functionality by increasing dietary threonine nutrition of a laying hen.